High temperature, incomplete combustion of a hydrocarbon such as petroleum, natural gas and other well known materials produces carbon black. When separated from the reaction gases, the product is a fluffy, carbon black powder.
In a typical furnace process for the production of carbon black, a fuel, an oxidant such as air, and a feedstock are reacted to provide a hot stream of combustion gases containing carbon black therein. The combustion gas stream is then quenched to a lower temperature by means of a water spray. The black is separated from the stream of gases in which it is suspended by known techniques, such as by cyclones and filters, and then conveyed to a pelletizer and subsequently dried.
Often, a short-term storage tank, called a surge tank, is located between the collection equipment and the pelletizing equipment to aid in providing a steady feed of carbon black to the pelletizer. A typical tank has a height of 10-15', the upper portion of said tank being cylindrical with a diameter of about 9'. The height of the cylindrical portion of the tank is approximately 3/4 of the total height of the tank. The lower remaining portion of the tank is in the form of a truncated cone, with a diameter decreasing from 9' at the top-most portion of the cone to between 4.5-6' at the flat bottom of the tank. The carbon black, which may be in the form of dry powder, moist powder and/or reprocessed pellets, enters at the top of the tank and is emitted through outlets at the bottom of the tank into one or more pelletizers where the carbon black is formed into pellets.
Carbon black can be formed into pellets by the well-known technique of wet-pelletization. Wet-pelletization is a process whereby carbon black material is formed into beads or pellets of increased density, cohesive strength and nondusting characteristics. In this process, carbon black is wetted, usually with water, and agitated in a conventional pelletizer. One of the major control problems in the wet-pelletization of carbon black is that of maintaining a proper balance of the mass flow rates of pelletizing liquid and carbon black powder that are injected into the pelletizer so that optimum pellet moisture content is achieved. It is not difficult to control the mass flow rate of the pelletizing liquid since the density of the liquid does not change appreciably. The volumetric rate of carbon black can also be closely controlled. However, variations in the density of the carbon black are often significant and occur frequently. These variations in the density of the carbon black within the surge tank can cause the mass flow rate of the carbon black from the surge tank to the pelletizer to fluctuate. This fluctuation in mass flow rate can cause the moisture content in the resulting carbon black pellets to vary. Many types of equipment have been used to feed carbon black powder from the surge tank to the pelletizer but none have provided a dependable stable mass flow rate of carbon black from the surge tank into the pelletizer.